1. Technical Field
The present invention generally relates to an image forming apparatus using an electrophotographic processor, such as a laser beam printer, a facsimile machine, and a photocopier, and more particularly, relates to an image forming apparatus using an elastic photosensitive drum for an electrophotographic processor with a nip created between the photosensitive drum and a charge roller and a transfer roller for enhancing the charging and transfer characteristics.
2. Related Art
Electrophotographic developing processes are widely used in image forming apparatuses to produce images on recording media in response to video signals. Common examples of an electrophotographic printing apparatus are a laser beam printer, a copier, and a facsimile system which forms images on an individual sheet of paper through a series of electrostatic image-forming steps as disclosed, for example, in U.S. Pat. No. 4,876,572 for Image Recording Having A Removable Image Forming Case issued to Nagatsuna, U.S. Pat. No. 4,896,191 for Sheet Transferring Mechanism In An Electrophotographic Recording Apparatus issued to Ohyabu et al., U.S. Pat. No. 5,119,137 for Structure And Method Of Mounting Recording Units In Electrophotographic Recording Apparatus issued to Katagata, U.S. Pat. No. 5,255,053 for Image Forming Apparatus Having A Transfer Drum, An Image Member Cartridge And Exposure Means issued to Green et al., U.S. Pat. No. 5,512,976 for Image Forming Apparatus Having Rotation Resistance Adjusting Means For Adjusting Rotation Resistance On A Photosensitive Drum issued to Kamano, U.S. Pat. No. 5,570,160 for Image Forming Apparatus Having A Rotatable Photoreceptor issued to Miwa et al., U.S. Pat. No. 5,640,650 for Process Cartridge Including A Spaced Rolling Members Support Feature And Image Forming Apparatus Using The Same issued to Watanabe et al.
Generally, the process of electrostatic image forming includes charging a photosensitive drum to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photosensitive drum is exposed to a light image to record an electrostatic latent image on its surface. The latent image is then developed by applying toner from a developing unit onto the photosensitive drum which is subsequently transferred and fixed on a recording paper which is fed from a paper feeding unit. When a toner image is fixed on a recording paper, the toner image is first heated and fused onto the recording paper, and then naturally cooled so that it is fixed onto the recording paper.
One significant problem that frequently occurs in such an image forming apparatus is the excessive and uneven pressure often asserted by the charge roller and the transfer roller onto the photosensitive drum during an image formation which causes damage to the outer surface of the photosensitive drum and disrupts toner image on the photosensitive drum to reduce the print quality. Examples of conventional photosensitive drum designs with high durability for high quality images are disclosed in U.S. Pat. No. 5,132,200 for Electrophotographic Photoreceptor With Porous Anodized Al Layer And Process for Producing The Same issued to Fukuda, U.S. Pat. No. 5,218,405 for Photoreceptor Drum Runout Control Apparatus issued to Wong, U.S. Pat. No. 5,270,141 for Image Holding Member, And Electrophotographic Apparatus, Apparatus Unit, And Facsimile Machine Employing The Same issued to Ohtani et al., U.S. Pat. No. 5,504,558 for Electrophotographic Photosensitive Member, And Electrophotographic Apparatus And Device Unit Employing The Same issued to Ikezue, U.S. Pat. No. 5,485,250 for Electrophotographic Apparatus With Photosensitive Member Having Surface Layer Of Binder Resin And Fluoro And/Or Silicon Compound Particles issued to Kashimura et al. While the conventional photosensitive drum designs are effective in their own rights, I have noted that further improvement can still be contemplated.